This invention relates to a tubular film including circular, tubular, cylindrical, ring or belt type films used as a conveyance belt for conveying fine parts at predetermined positions assuring high-precision positional information, or used in an airtight container for containing a product or the like, and a tubular-film manufacturing method. The present invention can be mainly used as a functional part of an image forming apparatus.
Especially, the technique of the present invention is preferable to manufacture a fixing film of an image fixing unit used in an image forming apparatus such as a copier, a printer and a facsimile apparatus.
Known conventional tubular-film manufacturing methods are:
(1) Press heat-melt molding represented by an inflation method; PA1 (2) Casting and centrifugal molding methods of applying a predetermined amount of liquid-state resin or its precursor to inner circumferential surface or outer circumferential surface of a tubular mold, and through desolvent and chemical reaction, removing the formed film from the mold; PA1 (3) As proposed by Japanese Patent Application Laid-Open Nos. 63-34120 and 63-34121, a lining method of: rolling a film sheet around a core member, melt-joining both ends of the film, and lining the inner surface of a hollow tubular member with the roll of the film sheet; and PA1 (4) A method for manufacturing a polytetrafluoroethylene tubular member proposed by Japanese Patent Application Laid-Open No. 52-117377.
Note that as prior applications, Japanese Patent Application Laid-Open Nos. 3-25477, 3-266870, 4-9989 and 4-292680 by the present applicant are known.
In the heat-melt molding (1), when the tubular film formed by the inflation method is removed from the mold the film may be deformed. In a case where this tubular film is used as a fixing film of a fixing unit of an image-forming apparatus as shown in FIG. 25, he deformed part causes degradation of image quality.
Regarding the casting method and centrifugal method (2), to obtain a uniform film thickness, liquid-density management, dry and reaction atmosphere adjustment, and solvent processing at a drying step increase costs. In addition, for the centrifugal molding, a large-scale device must be used.
The lining (3) of the hollow tubular member can obtain a lining layer of a uniform thickness. However, to obtain a tubular film from the lining layer, separation of the film from the inner circumferential surface of the hollow tubular member may not be successfully done due to tight adherence between the film and the inner circumferential surface of the tubular member.
The main purpose of the conventional methods (1) to (5) is to manufacture a tubular film of a uniform thickness. When the tubular film of a uniform thickness obtained by any of methods (1) to (5) is rotated, meandering of the film occurs. To solve this problem, it is necessary to strictly manage measurement precision of drive roller and the like.